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Galileo's Telescope Galileo's telescope Here you will find all of the texts on application, compiled by the Institute and Museum of the History of Science, Florence. INDEX 1 HISTORY 3 1.1 The invention 3 1.2 From the workshop to the stars 4 1.3 The Keplerian telescope 7 1.4 The tube and the housing of the optical parts 8 1.5 Chromatic aberration 11 1.6 Reflecting telescopes 12 1.7 Chronology 15 1.8 Test 21 2 EXPLORE 22 2.1 The instrument 22 2.2 How it works 23 2.3 The modern telescope 25 2.4 Test 25 3 SIMULATION 26 3.1.1 The height of the mountains on the Moon 26 3.1.2 The satellites of Jupiter 26 3.1.2.1 Il micrometro 26 3.1.2.2 Jovilabe 27 3.1.2.3 Il celatone 27 3.1.3 The phases of Venus 28 3.1.4 Saturn’s system 28 3.1.5 Sunspots 29 3.1.5.1 The helioscope 29 3.1.6 The stars and the Milky Way 30 3.2 The performance of the telescope 30 2 1 HISTORY 1.1 THE INVENTION The question of who was the first to invent the telescope is as old as the instrument itself. On October 2, 1608, the Dutch Estates General examined an application for a patent for "a device to observe things at a distance" presented by a certain Hans Lipperhey (?-1619), an obscure spectacles-maker from Middelburg, in southwestern Holland. The patent application was rejected on the grounds that, although the usefulness of the device was recognised, especially for military purposes, it was deemed impossible to keep the secret of its construction for very long. And especially considering that, in those same days, another instrument-maker – a certain Sacharias Janssen (1588-1630), he too a spectacles-maker in Middelburg, indicated by Pierre Borel (c. 1620- 1671) a few decades later as the true inventor of the telescope – declared that he knew how to build the instrument. News of the invention spread rapidly throughout Europe, and already by April 1609 little telescopes about thirty centimetres long were to be found on sale, at the shops of spectacle-makers, in Paris and presumably in London. In Italy, the new instrument made its appearance at Milan in May of the same year, and two or three months later in Rome, Naples, Padua and Venice, where Fra Paolo Sarpi (1552-1623), a friend of Galileo, had heard news of it already by November 1608. IMAGES AND CAPTIONS 1. Galileo's telescope, late 1609 - early 1610, Florence, Institute and Museum of the History of Science. This is one of the only two surviving telescopes from the vast Galilean production, now conserved at the Institute and Museum of the History of Science, Florence. 2. Report of the October 2, 1608 session of the Dutch Estates General. On October 2, 1608 the Dutch Estates General discussed the patent application made by Hans Lipperhey (?-1619), a spectacles-maker in Middelburg, for the construction of telescopes. The Dutch government commissioned him to make six telescopes, but refused to grant him a patent. 3. Portrait of Hans Lipperhey. Pierre Borel, De vero telescopii inventore, The Hague, 1656. 3 A native of Wesel in western Germany, and spectacles-maker in Middelburg, southwestern Holland, Hans Lipperhey (?-1619) is considered one of the possible inventors of the telescope. 4. Geographical chart of Holland. Both Hans Lipperhey (?-1619) and Sacharias Janssen (1588-1630), by many deemed the real forerunners of the telescope, worked as spectacles-makers in Middelburg, southwestern Holland. 5. Diego Velasquez, The Surrender of Breda, 1635, Madrid, Prado Museum. The painting represents the surrender of Breda, which took place in 1625, after a long siege. Justin de Nassau consigns the keys of the city to the commander of the Spanish troops, Ambrogio Spinola (1569-1630), shown holding a field telescope. 6. Portrait of Sacharias Janssen. Pierre Borel, De vero telescopii inventore, The Hague, 1656. A spectacles-maker in Middelburg, southwestern Holland, Sacharias Janssen is indicated by Pierre Borel as the true inventor of the telescope. 7. Pierre Borel, De vero telescopii inventore, The Hague, 1656 - frontispiece. 8. Johannes Collarts, Plate depicting a sixteenth-century optician's shop, engraving, 1582. Already by April 1609 in the spectacles-makers' shops of Paris, and probably of London as well, small telescopes about thirty centimeters long were being sold. 9. Luigi Catani, Galileo with some of his pupils in Piazza San Marco, Venice, as he tests the first lenses with which he will construct his telescope, 1816, Florence, Palazzo Pitti, Gallery of Modern Art. 10. Portrait of Fra Paolo Sarpi. Natale Schiavoni, Cento ritratti di illustri italiani [One hundred portraits of illustrious Italians], Calcografia Bettoni, Milan, 1824. The Venetian Servite Fra Paolo Sarpi (1552-1623) met Galileo, probably in late 1592, and was in contact with him, actively following his research activities, until 1606, when the city of Venice was struck by an interdiction for heresy. 1.2 FROM THE WORKSHOP TO THE STARS Galileo (1564-1642) fabricated his first telescope, with only three magnifications, in the summer of 1609. But already on August 21 of that year, in the bell tower of San Marco, in the presence of the Doge and other Venetian notables, he presented an instrument that had eight magnifications, and that won him a lifetime appointment to the Padua Chair of Mathematics at a salary of one thousand florins a year. In November, Galileo had at his disposal a telescope with twenty magnifications, that is, more powerful by far that all the others circulating through Europe at the time, which utilised ordinary lenses made for spectacles, of low quality and with unsuitable focal lengths. The instruments developed by Galileo were highly superior in performance, for example, to the telescope with six magnifications with which the Englishman Thomas Harriot (1560-1621) had conducted observations and made drawings of the lunar surface in July 1609. Thanks to the power of his instrument, Galileo achieved exceptional results in his observations of the moon, demonstrating, in fact, that its surface is not perfectly spherical nor immaculate and even 4 managing to calculate the height of the lunar mountains. Subsequently, Galileo was to make the exceptional series of astronomical discoveries, described in the Sidereus Nuncius [The Starry Messenger] published in March 1610, and destined to revolutionize forever the traditional view of the cosmos. He was to discover, first of all, the existence of a myriad of new stars, showing that the Milky Way is "no other than a mass of innumerable stars scattered in clusters". And again, he was to observe the strange appearance of Saturn, whose true cause, the presence of a ring around the planet, was to be found by Christiaan Huygens (1629-1695) nearly half a century later. He was the first to observe the phases of Venus, which conclusively demonstrated that the planet moved, orbiting around the Sun. But the discovery that brought him immortal fame, in January 1610, was that of the four satellites of Jupiter, which Galileo, in homage to the dynasty that ruled Tuscany, named Astri Medicei, or Medicean Planets. IMAGES AND CAPTIONS 1. Justus Suttermans, Portrait of Galileo Galilei, 17th century, Florence, Uffizi Gallery. In the summer of 1609 Galileo (1564-1642), a reader in mathematics at the University of Padua, developed his first telescope, with a power of only three magnifications. 2. Guglielmo De Sanctis, Galileo Galilei showing his telescope to the Signoria of Venice, printed reproduction, Rome, Museum of Rome, detail. On August 21, 1609, on the bell tower of St. Mark's in the presence of the Doge of Venice and other Venetian notables, Galileo (1564-1642) presented a telescope with eight magnifications, which won him a lifetime appointment to the Chair of Padua and a salary of 1000 florins. 3. Engraving showing the University of Padua (in the background). Galileo Galilei's wooden professorial chair at the University of Padua (in the foreground). 4. Galileo's telescope, late 1609 - early 1610, Florence, Institute and Museum of the History of Science. 5 This is one of the two surviving telescopes from the vast Galilean production, now in the Institute and Museum of the History of Science, Florence. 5. Drawing of the lunar surface done by Thomas Harriot on July 26, 1609. 6. Portrait of Thomas Harriot. In 1609 Harriot (1560-1621) fabricated a telescope with six magnifications, with which he could observe the surface of the Moon. 7. Galileo Galilei, Sidereus Nuncius [Starry Messenger], autograph sketch, Mss. Gal. 48 –Div. 2a – Part III, tome 3, c. 28r. Representation in tempera of the lunar surface. 8. Galileo Galilei, Sidereus Nuncius [Starry Messenger], Venice, 1610. Drawing showing the Moon in the first quarter. 9. Galileo Galilei, Sidereus Nuncius [Starry Messenger], Venice, 1610. Drawing illustrating the method used to calculate the height of the mountains on the Moon. 10. Galileo Galilei, Sidereus Nuncius [Starry Messenger], Venice, 1610 - frontispiece. 11. Galileo Galilei, Sidereus Nuncius [Starry Messenger], Venice, 1610. Drawing of the Pleiades. 12. Letter from Galileo to Belisario Vinta, Padua, July 30, 1610. Drawing of "three-bodied" Saturn: "[…] the star of Saturn is not one alone, but is composed of 3, which almost touch one another, nor do they ever move or change position among themselves; […] the one in the middle being about 3 times larger than the two at the sides." 13. Letter from Galileo to Fortunio Liceti [in Padua], Florence, January 11, 1620. Drawing showing one of the aspects of Saturn. 14. Christiaan Huygens, Sistema Saturnium, The Hague, 1659. Diagram explaining the appearance of Saturn due to the presence of the ring.
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